An urgent problem for astronautics is still substantial reduction of specific costs of delivering cargoes into space—embodiment of many technologically feasible and important space projects is postponed because of unacceptable cargo transportation prices. A high price of cargo transportation from the Earth into cosmic space is generally caused by the fact that fuel makes up the greater part of rockets' cargo while the proportion of net cargo is measured by several percents. There were expressed different proposals on development of methods and systems aimed at solution of the problem of reduction in the price of delivering cargoes into space.
In judgment of some specialists, this problem may be obviated if energy and raw material resources of space itself, including those of near-earth space, are used for transportation of cargoes into space. There are two directions.
One of them consists in reduction of expenses in delivering cargoes into a near-earth orbit due to application of a suborbital single-stage rocket with small fuel consumption per one unit of mass of a cargo and an orbital accelerating spacecraft. A rocket imparts only a part of a speed necessary to insert the cargo into an orbit while the orbital accelerating spacecraft imparts a full orbital speed to the cargo. An orbital-based stage approaches a ground-based suborbital accelerating stage after preliminary aerodynamical braking and partial loss of the speed, and, after receiving the cargo, speeds up to the orbital speed again using a cheap fuel produced on moon factories (J. M. Es'kov, Environmentally Safe Global Power Industry and Astronautics in XXI Century//Moscow: “Trinitarizm Academy”, El 77-6567, publication 14590, Mar. 10, 2007; V. I. Florov, The Future of the Earth and Mankind: Role and Place of Astronautics//http://n113m.narod.ru/galaktika/florov.htm).
The essence of another direction consists in that the cargo (fuel components in our case) is taken directly from the atmosphere. At the same time, the method used for speeding the fuel components up to an orbital speed consists in transfer of necessary kinetic energy to accelerated gasses directly on board an orbit-based spacecraft. Such spacecrafts are provided with an electric rocket propulsion system where the speed of working substance outflow exceeds the speed of the incoming working substance. Thus, a high proportion of net load is provided in the total mass due to a small proportion of substances consumed in the electric rocket propulsion system. The necessary raw materials for rocket fuel components are extracted directly in the orbit from the atmosphere of a planet, e.g. the Earth, by low-orbit container spacecrafts (CSCs). Capture and accumulation of raw materials is performed as follows. The CSC moves within the atmosphere in a low near-earth orbit at an altitude of 105 to 120 km and collects rarefied air while extracting oxygen from it and using the remaining nitrogen in an electric jet engine to provide compensation for aerodynamic drag loss.
The project PROFAC (PROpulsive Fluid ACcumulator) by S. Demetriades is known as implementing the method considered above (K. Getland, Space Technology. Illustrated Encyclopedia. Translation from English.—Moscow: Mir, 1986).
A PROFAC apparatus includes an air intake (a receiving device), a componentry liquefaction and separation arrangement, liquefaction arrangement heat dissipaters, a liquid oxygen tank, additional fuel tanks, electric jet (electric rocket) engines, an accelerating engine, a docking unit, a nuclear reactor and reactor's heat dissipaters. When orbiting, PROFAC captures rarefied air near the boundary of dense layers of atmosphere, compresses it by means of gas-dynamic compression in the intake and compressors, cools it off and extracts liquid oxygen. PROFAC uses the remaining nitrogen in a nuclear electric jet engine to provide compensation for losses caused by the aerodynamic drag. The largest part of an external spacecraft surface is occupied by heat dissipaters to dissipate extra heat from a power generating unit, the compressors and the liquefaction arrangement. A standard rocket system is positioned on board the apparatus for transition into a higher orbit in emergency situations and for unloading carried out through the docking unit. PROFAC has got advantages over other known nuclear transport systems so far as it eliminates the necessity to dispose a heavy nuclear reactor on board of apparatus themselves. By estimation of its developers, use of such system can reduce the cost of delivering a cargo to the Moon to $1000 per 1 kg.
In spite of its economic attractiveness, disposition of an active nuclear reactor in an utmost low orbit in upper layers of atmosphere is the main drawback of the PROFAC system. In case if an emergency situation occurs in the nuclear reactor, the system stipulates transition into a higher orbit to repair or bury a defective reactor at a high altitude, however it doesn't guarantee complete safety of earth territories disposed under the orbit of the spacecraft.
Use of a satellite solar power station (SSPS) instead of the nuclear reactor in utmost low orbits is difficult so far as a large area of their members such as solar batteries or focusing mirrors, creates the aerodynamic drag of such a value that the power of the SSPS is not enough to compensate said drag, that makes the system unworkable. Higher orbits are required for efficient usage of solar energy, but a density of raw-material components in this case is so low that exploitation of CSCs turns unprofitable.
As one of possible variants of said disadvantage elimination, let us consider as a prototype method for accumulating atmospheric oxygen and nitrogen with the help of a low-orbit near-earth container spacecraft remotely supplied with power from middle-altitude energy-emitting laser facilities (Ju. M. Es'kov, Environmentally Safe Global Power Industry and Astronautics in XXI Century//Moscow: “Trinitarizm Academy”, El 77-6567, publication 14590, Mar. 10, 2007, p. 41-45).